Created attachment 8730208 [details] Screenshot showing the issue [Note]: - [Affected versions]: - Developer Edition 47.0a2 - Latest Nightly 48.0a1 [Affected platforms]: - Mac OS X 10.11.1 (Macbook with Retina display + another monitor 'fullHD or lower') [Steps to reproduce]: 1. Start Firefox on the second monitor 2. Move Firefox to Retina display [Expected result]: - No layout, theme issues can be seen, the scaling of items is properly done. [Actual result]: - Minimize, maximize and close icons are visible shrinked. [Regression range]: - I was unable to make mozregression work from some unknown reason (will try to make it work asap). I did a manual regression on mozilla-central tinderbox builds: Last good build: 2016-02-09 First bad build: 2016-02-10 https://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=d1a54ae63da7ebc4bc1eeb5b613e8ec29bfcb80a&tochange=2dfb45d74f42d2a0010696f5fd47c7a7da94cedb Please set the regressionwindow-wanted in keywords if a more indepth regression is needed. [Additional notes]: - Screenshot with the issue attached.
Jonathan, do you think this has something to do with per-monitor DPI feature? I know it's not supported on Mac but maybe something broke related to the feature might have broke this.
This sounds like bug 1247272 to me, which is a regression from bug 1243418.